Interpretive Summary: The acreage of cotton in the United States that is tolerant to the herbicide glyphosate has increased by 70% since its commercialization in 1997. Glyphosate herbicide controls most weed species common to cotton production. However, some species are relatively tolerant of glyphosate, so there is interest in identifying herbicides that can be mixed with glyphosate to improve control. Greenhouse and field studies were conducted at the Southern Weed Science Research Unit farm, Stoneville, MS to study potential interactions between glyphosate and trifloxysulfuron on control of several weed species. Barnyardgrass, browntop millet, prickly sida, sicklepod, and velvetleaf were controlled 73 to 99% with glyphosate alone and control was not improved by adding trifloxysulfuron. Mixing trifloxysulfuron and glyphosate increased control of pitted morningglory and hemp sesbania (73 to 88%) compared with glyphosate alone (45 to 66%). Mixing trifloxysulfuron with glyphosate has potential to improve control of troublesome broadleaf weed species in cotton without reducing glyphosate efficacy on other broadleaf and grass weed species.

Technical Abstract:
Greenhouse and field studies were conducted to evaluate potential interactions between glyphosate and trifloxysulfuron on barnyardgrass, browntop millet, hemp sesbania, pitted morningglory, prickly sida, sicklepod, and velvetleaf control as well as cotton injury. Glyphosate was tested at 560 and 1120 g ai/ha and trifloxysulfuron at 2.5 and 5 g ai/ha on two- to three-leaf and four-to six-leaf plants. Combinations of both herbicides were also evaluated at both rates and plant growth stages. Barnyardgrass and browntop millet control was not reduced when trifloxysulfuron was added to glyphosate. Barnyardgrass, browntop millet, prickly sida, sicklepod, and velvetleaf control with 1120 g/ha glyphosate was 85 to 99% at the 2- to 3-leaf growth stage and 73 to 99% at the 4- to 5-leaf growth stage. Addition of trifloxysulfuron to glyphosate did not improve control of prickly sida, sicklepod, and velvetleaf compared with glyphosate alone. Mixing high rates of trifloxysulfuron and glyphosate was additive in controlling 4- to 5-leaf pitted morningglory and hemp sesbania (73 to 88%) compared with 1120 g/ha glyphosate alone (45 to 66%). Trifloxysulfuron at 5 g/ha resulted in 20% injury to 2-leaf cotton and 2 to 15% injury to 4- to 5-leaf cotton. Mixing trifloxysulfuron with glyphosate has potential to improve control of pitted morningglory and hemp sesbania without reducing glyphosate efficacy on other broadleaf and grass weed species.